1. Field of the Invention
The present invention relates to a boat propulsion unit. More specifically, the present invention relates to a boat propulsion unit having an engine.
2. Description of the Related Art
Conventionally, a boat propulsion machine having an engine (boat propulsion unit) is known (for example, see JP-A-Hei 9-263294). JP-A-Hei 9-263294 discloses a boat propulsion machine having an engine and a power transmission mechanism for transmitting the driving power of the engine to a propeller by a specified fixed reduction ratio. This boat propulsion machine transmits the driving power of the engine directly to the propeller through the power transmission mechanism, and the propeller speed increases in proportion with an increase in the engine speed.
However, in the boat propulsion machine (boat propulsion unit) disclosed in JP-A-Hei 9-263294, when the reduction ratio of the power transmission mechanism is configured so that the maximum speed becomes large, it is difficult to improve the acceleration performance at a low speed. Conversely, when the reduction ratio of the power transmission mechanism is configured so that the acceleration performance at a low speed is improved, it is difficult to increase the maximum speed. That is, in the boat propulsion machine disclosed in the JP-A-Hei 9-263294, it is difficult to achieve both a performance of the acceleration and the maximum speed to approach a level desired by a user.
In order to solve such an inconvenience, generally, a boat propulsion unit including a power transmission mechanism having a variable speed mechanism portion is desired.
However, the boat propulsion unit having the above-described variable speed mechanism portion generally operates in a state where a gear and the like of the variable speed mechanism portion are soaked in oil for lubricating the variable speed mechanism portion. Consequently, the gear is prevented from rotating due to viscosity of the oil and the like, so that there is a problem that the loss of the driving energy of the engine occurs.